The present invention relates to devices and methods for measuring, in-vivo, the concentration of a constituent of a body fluid. In one embodiment, the present invention relates to a device and method for measuring, in-vivo, glucose concentration within the context of diabetotherapy.
Devices used in diabetotherapy for measuring the glucose concentration in the blood or in another human body fluid are based on a chemical reaction between the glucose and a reactant. The diabetic injects himself with a needle under the skin and brings the blood penetrating through the skin at the injection point into contact with the reactant. The reactant is applied to a test strip. The test strip, including the point at which the reaction between the glucose and the reactant has occurred, is inserted into a measuring and evaluation means. A detector which is sensitive to the reaction between the glucose and the reactant records the result of the reaction and outputs a signal dependent on the result of the reaction. The glucose concentration in the blood sample is determined from the signal and optically displayed. More basic measuring devices are based on a color change of the test strip, the tint of the test strip being a measure of the glucose concentration in the blood sample. A disadvantage of the method is that the skin must be broken or injected again for each measurement.
WO 98/01071 describes a measuring device using which the glucose concentration in the blood or in the intercellular fluid can be optically measured. The device comprises a light source and a light detector which operate in the infrared range. The light source and the light detector are implanted in the human tissue. Their arrangement when implanted is such that a decoupling area and a detector area, lying directly opposite each other in the tissue, form a measuring distance between them in which light is absorbed. Light emitted from the decoupling area is absorbed by the detector area, once it has passed along the measuring distance. Infrared light of various wavelengths is used, and evaluated by means of infrared spectroscopy. The degree of absorption of the infrared light is used as a measure of the glucose concentration in the blood. Implanting is complicated and invasive.